In general, an earth leakage breaker is an electrical wiring device that detects an electric leakage in an electrical circuit or device that uses electricity and, if a leakage current of more than a specific level is detected, cuts off power supply, thus preventing the human body from being damaged due to an electric shock, and preventing an electrical fire from occurring caused by the electric leakage.
It is reported that the most common electrical fires are caused by an electric leakage of a house (interior) wiring; however, since the earth leakage breaker operates when a leakage current is generated, it cannot not be assumed that the cause of the most common electrical fires is the electric leakage.
In fact, the most common electrical fires occur when an electric spark is generated by a contact failure of a wiring circuit, an insulation breakdown due to heat generation at a contact point, a momentary short circuit, or a high connection resistance. In this case, the earth leakage breaker may not be operated and, if there is an inflammable material near the electric spark, it may result in a disaster
However, it is difficult to inspect the contact failure of the wiring circuit contact point, and even experience experts can measure only a disconnection and a short circuit by a physical inspection or using a circuit tester.
Especially, when an electrical pipe is formed of synthetic resin (PVC), an insulation failure between electric wires in the pipe is not shown during insulation measurement, and the connection or contact failure of the electrical wiring cannot be checked before a malfunction occurs.
Moreover, the malfunction caused by the connection or contact failure of the electrical device that uses electricity may result in a considerable loss or disaster in the industrial field; however, it is very difficult to detect the same.
Meanwhile, since the conventional earth leakage breaker operates when a leakage current is continuously generated or when a current exceeding a rated current flows, it is impossible to prevent an electrical fire due to the contact failure of the contact point in the low voltage house wiring, the momentary short circuit, or a tracking between wires.
Here, the above contact failure, momentary short circuit, and tracking between wires will be described to examine their common features.
First, when the contact failure occurs, the insulating material of the wiring is deformed and the contact surface thereof is oxidized due to heat generated by the contact failure.
Accordingly, the connection resistance is increased more and more, and thereby an increase in connection heat is repeated. As a result, the insulating material is gradually carbonized or deformed to cause a short circuit between wires, and a flashover caused by the connection heat ignites an adjacent inflammable material, thus causing a fire.
Second, a very strong electric spark/arc is produced by a short circuit due to burn damage of an insulating coating or by a momentary short circuit due to a mistake during operation, thus causing a fire.
Especially, since the electric spark/arc has a low effective current, the operation of the earth leakage breaker may be delayed or it may not work.
Lastly, the electric spark/arc and flashover produced by the tracking between wires due to an insulation failure ignite an adjacent inflammable material to cause a fire.
The electrical fire occurring in the wiring system is accompanied with the overheat, electric sparks/arc, and flashover, and thus it develops in a very short moment.
Examining the characteristics of the current flow, since a very high current is rapidly changed in a unit time, the ascending and descending angles are close to a right angle, and such a current flows with an irregular impulse several times, and its effective current is very low.
In the case where the contact of the contact point in the wiring circuit is poor, the voltage supplied to a load side has an irregular impulse, and thus the current flows with an irregular impulse having a low effective current. Accordingly, it is difficult for a thermal or electromagnetic breaker to perform the cutoff operation.
That is, when the electric spark/arc having a low effective is generated, the breaking operation of the earth leakage breaker is not made.
As above, since the conventional earth leakage breaker operates in a state of an overload or electric leakage, it is impossible to prevent a disaster due to an electric spark/arc (flame) generated on an electric wire by an abnormal state such as a connection failure.
Accordingly, it is necessary to prevent a disaster due to an electric spark generated on an electric wire by an abnormal state such as a connection failure, which the conventional earth leakage breaker and the electronic switch cannot prevent.